I think the natural tendency is to drift towards the middle in terms of effort. What I mean by this is that athletes often make their hard efforts too easy and their easy efforts too hard. But I think that gadgets can help an athlete make their hard efforts appropriately challenging, to tax the system effectively and to stray away from doing ‘junk’ sessions where you’re neither here nor there. They’re also useful in keeping the easy efforts honest, but not so hard that they may negatively impact your hard efforts in the days afterwards.
I almost never ditch the gadgets but sometimes I will stop looking at them. For example: I may have a target wattage of 250W for my easy ride, but some days I’m just too tired to push that. On one of those days I’ll switch my Garmin over to the cadence-only screen and do the remainder of the ride on feel.
The same is true on an easy run that’s not going to plan, although I won’t do this on the hard efforts. If I’m doing a V02 max workout with a target power between 410-440W, and I can’t get inside of that zone, I won’t continue the workout with sub-par numbers. In that scenario, I’m too tired to tax the V02 max on that day so will perhaps switch the ride to an easy one or just stop altogether. The same is true for run interval workouts, I’d prefer to switch the session up rather than suffer unnecessarily.
The only other time I’ll stop looking at the gadgets is if a race isn’t going to plan. If I have a target wattage on the 70.3 bike and within a few kms of riding that wattage is massively taxing, I’ll often throw that plan out of the window and ride most of the bike on feel (but still watching the power meter on the climbs to make sure my power isn’t spiking too much).
All in all, I think the only time you should completely ditch the gadgets is during those swims, rides and runs that are purely for joy, i.e. no training effect is intended.